1. Technical Field
The present invention relates to a surface mounting base for an oscillator that uses a J lead terminal, and to a crystal oscillator that uses the surface mounting base (hereinafter, referred to as a “surface mounted crystal unit”), and in particular to a surface mounted crystal unit having excellent compatibility with a set substrate that mounts the surface mounted crystal unit.
2. Background Art
Since a surface mounted crystal unit is small in size and is light weight, it is used particularly inside portable electronic devices. Usually, a crystal element is mounted on a surface mounting base and is hermetically sealed. Recently, a surface mounting base that takes into consideration its compatibility with a set substrate on which the surface mounted crystal unit is mounted, has been proposed (see Japanese Unexamined Laid-open Patent Publication No. 2003-297453).
FIG. 5 is a diagram for explaining a conventional example, wherein FIG. 5A is a vertical sectional view of a conventional surface mounted crystal unit, and FIG. 5B is a plan view of the crystal element thereof.
As shown in FIG. 5A, the surface mounted crystal unit is constructed such that a crystal element 2 is mounted on a surface mounting base 1 and is covered and hermetically sealed with a cover 3. The surface mounting base 1 comprises an insulation base 4, lead terminals 5, and a sealing glass 6. The insulation base 4 is made from alumina ceramic for example, and has a pair of through holes 7 on its opposite end sides. In these pair of through holes 7, the sealing glass 6 with the lead terminals 5 passing therethrough, is embedded in gaps between the through holes 7 and the lead terminals 5, forming a so-called airtight terminal.
Each lead terminal 5 is made from metal such as Cu, and has a crank shaped cross-section as shown in FIG. 5A, and comprises a holding part 5a, a through part 5b, and a mounting terminal part 5c. The holding part 5a and the mounting terminal part 5c are formed bent in horizontally reversed directions on the top and bottom sides of the through part 5b, as shown in the diagram. The sealing glass 6 is made from solid state powdered glass, and is poured into the pair of through holes 7, and is melted integrally with the insulation base 4 and the lead terminals 5.
Moreover, the crystal element 2 is, for example, an AT-cut crystal as shown in FIG. 5B. Its both principal surfaces have an excitation electrode 8, from both ends of which extension electrodes 9 extend. In addition, both end parts of the crystal element 2 from which the extension electrodes 9 extend are fixed to the holding part 5a of the lead terminal 5 by an electrically conductive adhesive (not shown). The cover 3 is made from insulating material such as ceramic, and as shown in FIG. 5A, is bonded on the periphery, which is one principal surface side of the surface mounting base 1 (insulation base 4), by glass sealing for example.
In such a conventional surface mounted crystal unit, as shown in FIG. 5A, the mounting terminal part 5c of the lead terminal 5 is bonded on a circuit terminal part of a set substrate (not shown) by means of soldering for example. In this case, since the mounting terminal part 5c is made from metal and has elasticity, it absorbs any difference in an expansion coefficient, between the surface mounting base (ceramic) 1 and the set substrate (such as a glass epoxy substrate). Therefore, when the surface mounted crystal unit is in use, external impact acting on the bonding part between them (the surface mounting base and the set substrate) due to heat cycling and the like is lessened, and for example, the generation of a crack or chip that might occur in the solder is prevented. As a result, the compatibility between the surface mounting base 1 and the set substrate becomes excellent.
However, in the surface mounting base 1 of such a conventional surface mounted crystal unit, first the lead terminals 5 are inserted into the through holes 7 and are clamped using a jig, and powdered glass is poured into the through holes 7 and is melted to integrate them. However, there has been a problem in that the through parts 5b of the lead terminals 5 are loose in the hollow part in the through holes 7 and their positioning becomes unstable, causing difficulty in manufacturing.
In consideration of such a problem, a surface mounting base shown in FIG. 6 has been devised. Here FIG. 6A is a vertical sectional view of another conventional surface mounted crystal unit, and FIG. 6B is a transverse sectional view (partial enlargement) along the line A—A of FIG. 6A.
In this conventional example, an insulation base 4 that functions as a surface mounting base, comprises an annular casing wall 4a having a single through hole 7. Furthermore, a pair of lead terminals 5 is made from Cu, and is constructed such that a folded part 5d is added to a holding part 5a, a through part 5b, and a mounting terminal part 5c. A projection 10 formed on the through part 5b, and an elbow shaped part of the folded part 5d are elastically contacted with the outside and inside of the insulation base 4 (casing wall 4a). Here, the lead terminal 5 is referred to as a J lead terminal that clamps the casing wall 4a (insulation base 4) (for information about J lead terminals refer to FIG. 15 and its description in http://www.lodestonepacific.com/techlib/tmappnotel.html).
In other words, the J lead terminal 5 passes through the sealing glass 6 and clamps the inside and outside of the annular casing wall 4a (insulation base 4), and has the holding part 5a for the crystal element 2 positioned above the top surface 6a of the sealing glass 6, which is one principal surface side of the insulation base 4. Moreover, the J lead terminal 5 is formed from the through part 5b which is embedded in the sealing glass 6, and projects from the bottom surface 6b of the sealing glass 6, the mounting terminal part (tip end part) 5c which extends from the inside of the annular casing wall 4d across the tip end surface to the outside of the annular casing wall 4a, and bends in a concave shape, and the folded part 5d. The J lead terminal 5 is soldered onto the insulation base 4.
Here, a slit 12 is provided in the center area on the through part 5b of the J lead terminal 5, and first and second bifurcated through parts 5b1 and 5b2 are formed. Moreover, the first and second bifurcated through parts 5b1 and 5b2 respectively have projections 10 that contact with the inside of the casing wall 4a (base 4). In a condition with the J lead terminal 5 which is bent in a concave shape, elastically clamped to the insulation base 4, and the tip end part (mounting terminal 5c), which is the flat bent part, pressed against the tip end surface 4b of the annular casing wall 4a (base 4), solid state powdered glass is filled into the single hole 7, and the sealing glass 6 is fired to integrate them.
In this case, since the J lead terminal 5 elastically clamps the inside and outside of the insulation base 4, disengagement of the J lead terminal 5 from the insulation base 4, or movement can be prevented without requiring a jig. Furthermore, since the projection 10 is provided on the through part 5b of the J lead terminal 5, a gap is created between the inside of the insulation base 4 (annular casing wall 4a) and the J lead terminal 5. In addition, the through part 5b of the J lead terminal 5 is constructed from the first and second bifurcated through parts 5b1 and 5b2, and the slit 12 is provided between them. Therefore, in the through hole 7, the molten glass readily enters into the gap with the inside of the casing wall 4a, from both sides of the through part 5b and from the center slit 12. As a result, manufacturing of the surface mounting base becomes easier.
Furthermore, since the through hole 7 formed in this insulation base 4a is a single one, a large amount of powdered glass can be filled thereinto. Therefore, molten glass will readily enter the gap between the insulation base 4 and the lead terminal 5 at the time of melting, thus realizing an effect that manufacturing can be made even easier. This effect becomes greater when the size of the insulation base 4 is small and the amount of powdered glass to be filled is small.
However, in the surface mounted crystal unit of this other conventional example, even though the tip end part 5c of the J lead terminal 5 is contacted against the end surface of the annular casing wall 4a (base 4), in practice a micro-gap c is created between them as shown in FIG. 7. Therefore, when the powdered glass is melted, molten glass enters the gap beneath the bottom surface 4b of the base 4 from the inner surface of the annular casing wall 4a (area indicated by P in FIG. 7) by capillarity, as shown in the partially enlarged vertical sectional view of FIG. 7, so that the bottom surface of the casing wall 4a and the mounting terminal part (tip end part) 5c are integrated. As a result there has been a problem in that a free motion surface of the mounting terminal part (tip end part) 5 between the annular casing wall 4a and the tip end surface (bottom surface) is reduced (elasticity is reduced), and the absorbance of distortion (stress) when it is mounted on the set substrate is decreased.
Consequently, an object of the present invention is to provide a surface mounting base of enhanced compatibility, which prevents distortion when mounting a surface mounted crystal unit onto a set substrate, and to provide a highly reliable surface mounted crystal unit that uses this surface mounting base.